The present invention relates to a vehicle occupant restraint system that is provided in a vehicle seat, and in particular to a vehicle occupant restraint system for preventing the submarining or slipping forward of the vehicle occupant under the seat belt in an impact situation such as a vehicle crash.
The term xe2x80x9csubmariningxe2x80x9d means the slipping forward of a vehicle occupant under the seat belt in an impact situation such as a vehicle crash in case the lap belt fails to restrain the pelvis of the vehicle occupant. This occurs most frequently when the vehicle occupant is sitting on an edge of the seat and/or the seat back is significantly reclined, and could impair the restraining capability of the seat belt because the seat belt fails to restrain the proper part of the vehicle occupant.
A copending U.S. patent application Ser. No. 09/526,405 filed Mar. 15, 2000 discloses a vehicle occupant restraint system in which a forward slip preventing member is moveably supported by a pair of casings fixedly attached to either side of a seat frame at a front part of a seat bottom so as to selectively project upward. The front end of the seat is raised only in case of an impact situation such a vehicle crash by actuating this forward slip preventing member with a power unit. The contents of this copending application are hereby incorporated in this application by reference.
Because the power unit produces a significant force at the time of its activation, the structural members of the system are required to withstand the resulting reaction force. However, the system is required to be compact enough to be installed in a limited space of a vehicle seat. The system is also desired to be inexpensive for the system to be accepted by the consumers.
In view of such problems of the prior art, a primary object of the present invention is to provide an anti-submarine vehicle occupant restraint system which is compact and light-weight.
A second object of the present invention is to provide an anti-submarine vehicle occupant restraint system which is easy and economical to manufacture.
According to the present invention, such objects can be accomplished by providing a vehicle occupant restraint system provided in association with a vehicle seat for preventing a vehicle occupant from slipping forward under a seat belt in an impact situation such as a vehicle crash, comprising: a pair of fixed support members attached to either side of a seat frame at a front part of a seat bottom; an arm pivotally attached to a front end of each of the fixed support members; a cross member extending between free ends of the arms; and a power unit provided in association with at least one of the support members for actuating the arms and cross member upward so as to selectively raise a front part of the seat bottom in an impact situation such as a vehicle crash; at least one of the support members comprising a main member having a vertically extending section which is elongated in a fore-and-aft direction, an upper flange extending laterally from an upper end of the vertically extending section, and a lower flange extending laterally in a same direction as the upper flange from a lower end of the vertically extending section, and a lid member which is attached to free ends of the upper and lower flanges to form a closed profiled casing in cooperation with the main member.
The hollow structure of the casing provides a high level of mechanical strength, and the two piece structure of the casing allows the assembly work to be performed in a simple manner because the components can be installed from sideways one after another in a relatively simple manner. Likewise, each of the arms may comprise a substantially horizontal web and a pair of arm flanges depending from either side or the web. Preferably, both the casing and arm are formed by stamp forming sheet metal. The pivot shaft for the arm may be passed through the vertically extending section of the main member, the lid member, and the arm flanges. According to a preferred embodiment, the pivot shaft consists of a hollow collar through which one of the mounting bolts for the casing is passed. The other mounting bolt may be passed through a suitable part of the casing. The side flanges of the arm extend along either outer or inner surfaces of the vertically extending section of the main member and the lid member.
Preferably, the power unit comprises a pyrotechnic cylinder unit which is received in the closed profiled casing and extends in the fore-and-aft direction, and a piston rod which is adapted to be actuated by the cylinder unit and engages a point of the corresponding arm offset from a pivot point at which the arm is attached to the casing. The pyrotechnic cylinder unit may be engaged by a pair of shoulders formed in the casing which, for instance, may be defined by edges of openings formed in the casing.
To simplify the arrangement, the lid part of the support member may comprise a part of the seat frame.
For the restraint system to be effective in use, the system may comprise a lock mechanism for retaining a corresponding one of the arms in the upwardly actuated state. It may be provided in each of the casino while the power unit is provided only in one of the casing. The casing typically receives therein a rod which extends in the fore-and-aft direction and engages a point of the corresponding arm offset from a pivot point at which the arm is attached to the support member, and the lock mechanism receives the rod so as to permit a sliding motion of the rod in a direction corresponding to a rising motion of the arm but prevent a sliding motion of the rod in an opposite direction. The rod may extend either rearward or forward from the point of engagement to the arm.